The present invention relates to a process for the manufacture of polymers in bead form from water-soluble, ethylenically unsaturated monomers by the inverse suspension polymerization process, in which an aqueous solution of the monomers is suspended in an inert hydrophobic liquid and is polymerized therein in the presence of a polymerization initiator and of a protective colloid, to give polymeric products in bead form.
This process for the manufacture of polymers in bead form from water-soluble, ethylenically unsaturated monomers is disclosed in German Pat. No. 1,081,228. For carrying out the process in practice, the correct choice of a suitable protective colloid is critical. The protective colloids stabilize the water-in-oil emulsions and influence the size of the polymer beads. Examples of protective colloids employed are sorbitan esters, eg. sorbitan monostearate and sorbitan monooleate, oxyethylated fatty acid amides, fatty acid esters of glycerol, sorbitan sesquioleate or sorbitan monooleate together with dicalcium phosphate or hydroxyapatite or silicates. A further group of conventional protective colloids comprises block polymers or graft polymers which contain at least one polymeric hydrophilic portion and one polymeric hydrophobic portion in the molecule. The inverse suspension polymerization process makes it possible to manufacture polymers having particularly high molecular weights and also makes it possible, given a suitable choice of the auxiliary phase, to remove the water directly from the system by azeotropic distillation.
During the polymerization, the aqueous phase of the water-in-oil dispersion passes through a very tacky state. Even after completion of the polymerization the suspended water-containing polymer is not tack-free. As a result, polymer particles can stick to one another and to the walls of the vessel during the polymerization or during the azeotropic dehydration which may be carried out after the polymerization. In extreme cases this phenomenon can reach the point of the entire polymer sticking together in a coherent mass which clings to the stirrer and the walls. The conventional protective colloids have the disadvantage that they do not prevent the formation of deposits on the walls of the polymerization apparatus and on the stirrer.
It is an object of the present invention to provide protective colloids for the inverse suspension polymerization process, described above, by means of which the disadvantages of the conventional protective colloids can very substantially be avoided.